The present invention relates to fiber cables and more particularly to an improved fiber cable employing loose tubes for carrying the fibers.
Optical fiber transmissions have the advantage, among many other ones of their immunity to electrical interferences as the information being transmitted is in the form of light pulses. As an optical fiber is composed entirely of dielectric materials it is not affected by electric signals or rust effects as most of the conductor metallic materials are.
Optical fibers are packed together and protected by a jacket to form an optical cable. Depending on the type of application, the requirements on the cable construction can be different. In some cases no special dielectric or noncorrosive requirements must be fulfilled, and the cable can include metallic components such as strength members or moisture resistant barriers. In other applications, however, some specific requirements can be needed and thus, an all dielectric cable will be necessary to be designed. An all dielectric cable does not attract lightning.
An essential component of the optical cables is the strength member which supports most of the tension that is necessary to apply to the cable during the installation work or during the cable operation.
Very few materials have been found, among the dielectric ones, with enough tensile strength and low elongation as to qualify them as strength members to be used in optical cables. For this reason, the price of these few products is very high.
On the other hand, when the size and weight of the cable are relatively large, the diameter of the strength member required is so large that the flexibility of the final cable is seriously impaired.
These advantages have been found particularly crucial when designing fully dielectric loose tube cables, as will be further explained.
The prior art was cognizant of certain of these problems and there are many patents and articles directed towards the protection and use of fibers in cable structures. See U.S. Pat. No. 4,038,489 issued on July 26, 1977 to D. W. Stenson, et al. and entitled CABLES. This patent shows a cable for dielectric optical waveguides or fibers, the fibers are arranged in segmented compartments. Tensile members are provided in the core of the cable and/or externally of the segmented compartments. Other patents such as U.S. Pat. No. 3,865,466 entitled OPTICAL GUIDES issued on Feb. 11, 1975 to R. J. Slaughter and depict a cable having an elongated central core consisting of at least one non-optical reinforcing member, a plurality of optical bundles arranged together in at least one stranded layer about the core and surrounding the stranded body there is an outer protective sheath. Still other patents such as U.S. Pat. Nos. 4,072,398 and 4,199,244 depict various cable formats for protecting the optical fibers while employed in a cable construction.
In any event, in constructing a cable employing fiber optics there is a desire to provide the cable with proper supporting structures and to completely eliminate any metal or electrically conducting components. In this way the cable is completely dielectric. Thus a growing number of users of fiber optic cables want to retain the dielectric characteristics of the optical fibers and avoid the use of metallic members such as steel strength members.
Hence many cable manufacturers fabricate such cables using Kevlar, Epoxy or Polyester impregnated Kevlar rods and Epoxy or Polyester impregnated "S" or "E" glass rods. These materials are relatively expensive and difficult to obtain.
It is of course a major factor in the production of such cables to keep the cost down while not departing from the electrical and mechanical properties of the product. Thus if one can reduce the cost of the dielectric strength members, one can achieve a lower cost for the optical cable.
It is therefore an object of the present invention to provide an optical fiber cable capable of being produced at a lower cost while maintaining proper strength and operating characteristics.